In the middle of this hubbub, David Ng, an agricultural specialist with U.S. Customs and Border Protection, tries to find things that are small and alive: snails, moths and weed seeds of all sorts.

It's part of a long-running struggle to protect America's fields and forests from exotic insects and weeds. That struggle plays out every day in seaports and airports across the country. There have been many failures in that struggle, but a few weeks ago, the inspectors also experienced a small victory.

On that day, Ng opened the steel door of a shipping container to inspect a load of organic soybeans from China and spotted a feathery little alien. "It was just kind of on top of the grain," he says.

It was a black and white moth, just a half-centimeter long. As the inspection continued, Ng found a few more. "It was not a moth that we had seen before, that I recognized or that any of the other inspectors recognized," he says.

He captured the insect, put it into a little glass vial, and shipped it off to experts at the U.S. Department of Agriculture.

They identified it as Nemapogon gersimovi, a kind of moth that had never been previously seen in the U.S. It likes to feed on seeds and grains.

"This was a very important detection," says Michael Raupp, an entomologist at the University of Maryland.

Nobody knows exactly how much of a problem that new moth from China might have turned out to be, he says. But previous invasive species have caused about $120 billion in damage every year, "so we simply don't need one more of these guys in here."

CBP gave the importer of those soybeans a choice: Destroy the beans or get them out of the country. In the end, the soybeans went back to China.

Inspectors can't possibly look at every incoming shipment. They focus on the shipments that they believe are most likely to contain pests, based on past history.

On the morning I arrived, it was a container of organic wheat from Argentina.

Ng snaps a plastic seal on the container with a bolt cutter and swings open the container's steel door. Some wheat spills out.

"Now we'll kind of sift through it a little bit," Ng says, "see if we see anything that stands out — any movement, or any other contaminants that pop out or look out of the ordinary."

Amanda Furrow, another CBP agricultural specialist, pours samples of the wheat into a set of sieves and shakes the grain back and forth, stopping every few seconds to stare intently. She picks something out, carefully. It's not wheat. It's a seed from the oat family, which includes at least one species that the government considers a "noxious weed."

"We'll send this to a USDA botanist, and they'll come back to us and let us know what species it is and if we need to take any further action," Ng says. They usually get a response within a few hours.

Nationwide, CBP inspectors find hundreds of insect pests and weed seeds every day. Others probably slip through, but Raupp says it's not a futile effort. Every successful detection is a small victory.

"It's vitally important," he says. "It's a good fight that we have to keep on fighting, I think."

Inspectors have, in fact, managed to keep some pests out of the country, such as the voracious Khapra beetle. Border inspectors catch about 200 of these insects every year. The Khapra beetle can be found in Asia, Africa and the Middle East. But at the moment, not in the United States.

As for that shipment of Argentinian wheat, it came through the inspection cleanly. That wild oat seed wasn't anything to worry out. This container will leave the port and go on to help satisfy America's appetite for organic bread.

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Transcript

LINDA WERTHEIMER, HOST:

Every day U.S. Customs Customs and Border Protection inspectors peer at fresh flowers and containers full of grain looking for alien invaders - snails, moths and weeds of all sorts. It's part of a long-running battle to protect America's environment from exotic invaders. There've been many failures in that struggle. NPR's Dan Charles has the story of a recent success.

DAN CHARLES, BYLINE: Baltimore seaport is a world of big, noisy steel machines, giant cargo ships, cranes and roaring trucks. And in the middle of all that David Ng, a Customs and Border Protection officer, is trying to find something small and alive. He's about to look inside a big, brown shipping container that just arrived from Argentina. He snaps a plastic seal with a bolt cutter, then swings open the container's steel door. Some wheat spills out. This is organic wheat.

DAVID NG: You know, we kind of sift through it little bit - sift through the grain, see if we see anything else that stands out as far as any movement or any other contaminants that pop out and look out of the ordinary.

CHARLES: A few weeks ago, David Ng was taking a look inside a container just like this one, filled with organic soybeans from China, and he spotted a feathery, little alien.

NG: It was kind of just on top of the grain there when we were doing our inspection.

CHARLES: It was a moth just half a centimeter long, colored black and white.

NG: It was not a moth that we had seen before that I'd recognize or any of the other inspectors here recognized.

CHARLES: He captured the insect, put it in a little glass vial and shipped it off to experts at the U.S. Department of Agriculture. The word came back this kind of moth had never been seen before in the U.S., and it likes to feed on seeds and grain.

MICHAEL RAUPP: This was a very important detection.

CHARLES: That is Michael Raupp from the University of Maryland. He studies invasive insects. Over the years, he says dozens of pests have come here from abroad threatening crops and entire ecosystems.

RAUPP: The cottony cushion scale threatened California's citrus industry - soybean aphids, the European corn bores. And now we have this egregious emerald ash borer.

CHARLES: No one knows exactly how much of a problem that new moth from China might have turned out to be, he says. But we know how much damage other invasive creatures have caused, probably around $120 billion every year.

RAUPP: So we simply don't need more and more of these guys in here.

CHARLES: U.S. Customs and Border Protection gave the importer of those soybeans a choice, either destroy the beans or get them out the country. In the end, the soybeans went back to China. Inspectors can't possibly look at every container that comes through here. They say they focus on the shipment most likely to contain pests, such as this container of organic meat from Argentina.

CHARLES: Amanda Furrow, another Customs and Border Protection officer, pours samples of wheat into a set of sieves, shakes the grain back and forth and stops every few seconds to stare intently.

AMANDA FURROW: A lot of times as we're sifting through, we'll find different types of federal noxious-weed seeds that would require action.

CHARLES: So not just insects.

FURROW: Right, yeah, 'cause there are certain seeds that would require action just the same as bugs would.

CHARLES: She picks something out carefully. I probably wouldn't have noticed it. But once I took a closer look, I can see it's not a grain of wheat, it's a kind of wild oat seed. David Ng says maybe it's allowed in the country, maybe not.

NG: We will send this to U.S. Department of Agriculture botanists, and they will come back and let us know what species it is and if we need to take any further action.

CHARLES: Nationwide, Customs and Border Protection inspectors find hundreds of insect pests and weed seeds every day. Others probably slip through, but Michael Raupp at the University of Maryland says each pest they do keep out of the country is a small victory.

RAUPP: It's vitally important. It's a good fight that we have to keep on fighting, I think.

CHARLES: And they have in fact managed to keep some pests out of the country. The voracious Khapra beetle for instance, border inspectors catch about 200 those insects every year. The Khapra beetle can be found in Asia, Africa and the Middle East, but right now not in the United States. As for that shipment of wheat that came through the inspection cleanly, the wild oat seed was not anything worry about. This container will now leave the port and go on to help satisfy America's appetite for organic bread. Dan Charles, NPR News. Transcript provided by NPR, Copyright NPR.